Any distributor collecting the tax on transactions exempt or not taxable under this chapter shall transmit to the Commissioner such erroneously or illegally collected tax unless or until he can affirmatively show that the tax has since been refunded to the purchaser or credited to his account. Any distributor who neglects, fails, or refuses to collect such tax upon every taxable sale made by him, his agents, or his employees shall be liable for and pay the tax himself, and such distributor shall not thereafter be entitled to sue for or recover in the Commonwealth any part of the purchase price from the purchaser until such tax is paid. Moreover, any distributor who neglects, fails, or refuses to pay or collect the tax herein provided, either by himself or through his agents or employees, is guilty of a Class 1 misdemeanor. All sums collected by a distributor as required by this chapter shall be deemed to be held in trust for the Commonwealth.